The effect of sunflower pollen age and origin on pathogen infection in the common eastern bumble bee (Apidae: Hymenoptera)

Bumble bees are globally important pollinators, contributing hundreds of millions of dollars annually in crop pollination services. Several species are in decline, making it paramount to understand how pathogens and nutrition shape bee health. Previous work has shown that consuming sunflower pollen (Helianthus annuus) dramatically reduces infection by the trypanosomatid gut pathogen, Crithidia bombi, in the common eastern bumble bee (Bombus impatiens). Sunflower pollen may therefore be useful as a dietary supplement for reducing this pathogen in managed bumble bee colonies. Here, we assessed the efficacy of freezer-stored sunflower pollen that was collected in different years and locations for reducing pathogen infection. We tested sunflower pollen that was 1, 3, 4, or 5 yr old and from sunflowers grown in the United States or China against a control of 1-yr-old buckwheat pollen from China, since buckwheat pollen results in high infection. We hypothesized that older pollen would have weaker medicinal effects due to degradation of pollen quality. We found that all sunflower pollen treatments significantly decreased Crithidia infection compared to controls. These results suggest that sunflower pollen can be freezer-stored for up to 5 yr and sourced from a wide range of geographic areas and still maintain its medicinal effects against Crithidia in the common eastern bumble bee. This is helpful information for stakeholders who might administer sunflower pollen as a dietary supplement to manage Crithidia in commercial bumble bee colonies.